The present invention relates generally to fabrication of semiconductor devices, and more particularly to reducing contamination, electromigration, and corrosion of conductive material during fabrication thereof.
Integrated circuits fabricated on semiconductor substrates for Ultra Large Scale Integration (ULSI) require multiple levels of conductive interconnections for electrically connecting the discrete semiconductor devices that comprise the circuits. Conventionally, the multiple levels of interconnections are separated by layers of insulating material. These interposed insulating layers typically have etched via holes which are used to electrically connect one level of metal to another. Typically, the conductive interconnection material is aluminum, titanium, tungsten or tantalum. As device dimensions decrease and device densities increase, however, conductive materials having lower resistivity, such as copper, are employed.
One well-known method for creating integrated circuits such as those described above is by chemical vapor deposition (CVD). Typically, a precursor gas is mixed with a carrier gas and introduced to a deposition chamber at an elevated temperature. Upon contact with a substrate (e.g., a semiconductor wafer) within the chamber, the precursor gas decomposes into various elements and reacts with the surface to create the desired material (e.g., an insulative layer such as an oxide, or conductive material such as copper). Such processes may also be enhanced by the use of a plasma within the chamber which provides for a more uniform deposition process, for example, when filling an opening in an oxide layer with conductive material. However, deficiencies in the CVD process may create undesirable results. It has been found typically that between the time that a conductive material is deposited upon the substrate and an insulative or barrier layer is deposited over the conductive material, the conductive material is subjected to an oxidation reduction reaction. For example, the topmost exposed surface of a copper interconnect is reduced to copper oxide. Such surface oxides inhibit the adhesion of further material layers (e.g., an insulative layer such as a nitride layer) that are deposited thereover.
One particular method known in the art for removing native oxides from conductive interconnects is by chemical removal of the native oxide. One conventional method for chemically removing an oxide from a copper layer is illustrated in FIG. 1, and includes the use of a hydrogen-based plasma. According to the conventional method 100, a semiconductor substrate is inserted into a process chamber at a predetermined temperature at 105. Chemically-reactive oxide-reducing gases such as ammonia (NH3) or hydrogen (H2) are then introduced into the process chamber at 110, and an oxide-reducing plasma is initiated by an application of a first RF power to the hydrogen-based oxide-reducing gases at 115. The oxide-reducing plasma chemically reacts with the oxide, and reduces the oxide to form copper (Cu) and byproducts (e.g., water (H2O) and hydroxide (OH)). These byproducts are then pumped out of the process chamber.
Nitride-forming gases, such as a mixture of silane (SiH4), ammonia (NH3) and nitrogen (N2), are subsequently introduced into the same process chamber at 120, and the first RF power is changed to a suitable second RF power at 125, thereby forming a second plasma suitable for CVD of a nitride layer over the copper. Following the formation of the nitride layer, the substrate is removed from the process chamber at 130.
Unfortunately, the conventional method 100 has several disadvantages. For example, adhesion of the nitride layer to the copper layer is adversely affected during this process because the silane may react with residual water or hydroxide that was not evacuated from the chamber. Such a reaction causes an undesirable hazy film to form over the conductive interconnect, thereby decreasing adhesion of the nitride layer to the underlying copper. Furthermore, a processing temperature in the chamber typically remains substantially constant, wherein hillock growth in the copper layer is accentuated by reducing the copper oxide at a temperature typically suited to the nitride deposition, thereby causing further undesirable effects in later depositions. Additionally, the copper and silane thermally react to form copper silicides (CuSix) when the plasma is turned off in preparation for subsequent process steps. Either of these films are undesirable for further depositions. Furthermore, modifying the RF power at 125 appears to induce plasma damage and antenna damage, and has deleterious effects on gate oxide integrity (GOI).
Therefore, there is a need in the art for a method of semiconductor device construction that reduces the amount of native oxide formation on the conductive material used to form the device, wherein the method mitigates the deleterious effects associated with conventional techniques.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention relates generally to improving an interface of a semiconductor substrate, and more specifically to a method of reducing an oxide formed over a metal layer and depositing a dielectric layer over said metal layer. The metal layer, for example, comprises a copper layer, wherein a native copper oxide is formed by oxidation of the metal layer. The dielectric layer, for example, comprises a nitride layer which is formed over the copper metal layer.
According to one exemplary aspect of the present invention, a method for improving an interface is provided, wherein two or more semiconductor substrates such as silicon wafers are provided, whereon a first layer has been formed. The first layer, for example, comprises a metal layer such as copper, wherein the first layer furthermore comprises an oxidized region. A first and second semiconductor substrate are consecutively inserted into a first process chamber, such as a plasma-enhanced chemical vapor deposition (PECVD) chamber, when the first process chamber is in a first loading position. A first processing position is then established, wherein the first and second substrates are processed. The first and second substrates are generally simultaneously subjected to a first temperature for a first predetermined period of time. The first and second substrates, for example, are placed on a first heated disk, wherein the substrates are subjected to the first temperature for a first soak time.
After the first soak time has generally elapsed, a first plasma is subsequently introduced into the first process chamber, wherein the first plasma is energized by a first predetermined power for a second predetermined period of time, thereby generally simultaneously chemically reducing the oxidized region of the first layer on the first and second substrates. The first loading position is then established again, and the first and second substrates are consecutively removed from the first process chamber.
According to one exemplary aspect of the present invention, prior to removing the first and second substrates from the first process chamber, a third and fourth substrate are consecutively inserted into the first process chamber when the first process chamber is in the first loading position, and the first processing position is again established. The first, second, third, and fourth substrates are then simultaneously processed in a manner similar to the previous processing of the first and second substrates, wherein the first and second substrates are processed a second time. According to another exemplary aspect of the present invention, the first loading position is again established after the first, second, third, and fourth substrates are processed, and a fifth and sixth substrate are consecutively inserted into the first process chamber. The first processing position is again established, and the first, second, third, fourth, fifth, and six substrates are then simultaneously processed in a manner again similar to the previous processing of the first and second substrates, wherein the first and second substrates are processed a third time and the third and fourth substrates are processed a second time. The first loading position is then established again for the consecutive removal of the first and second substrates from the first process chamber.
According to another exemplary aspect of the present invention, following the removal of the first and second substrates in the first process chamber, the first substrate is inserted into a second process chamber (e.g, a PECVD chamber) when the second process chamber is in a second loading position. A second processing position is subsequently established after insertion of the first substrate, wherein the first substrate is subjected to a second temperature for a third predetermined period of time in the second process chamber. For example, the first substrate is placed on a second heated disk, wherein the first substrate is subjected to the second temperature for a second soak time.
After the second soak time has generally elapsed, a second plasma is then introduced into the second process chamber, wherein the second plasma is energized by a second predetermined power for a fourth predetermined period of time, thereby forming a second layer over the first layer. The second layer, for example, comprises a generally insulative layer such as a nitride layer. The second loading position is then reestablished, and the second substrate is also inserted into the second process chamber. The second process position is then reestablished, and the first and second substrates are generally simultaneously processed in a similar manner as the first substrate was previously processed in the second process chamber, thereby forming the second layer over the first layer on the first and second substrates. The second loading position is then established again.
According to one exemplary aspect of the present invention, the first substrate is removed from the second process chamber, and the second processing position is again established. The second substrate is again processed in a similar manner as the second first and second substrates were previously processed in the second process chamber, thereby forming the second layer over the first layer on the second substrate. Accordingly, the interface between the first layer and the second layer on the first and second substrates has been improved. According to another exemplary aspect of the present invention, the third, fourth, fifth, and sixth substrates are consecutively inserted into the second process chamber prior to removing the first or second substrates, and the substrates are processed in a similar manner as the second first and second substrates were previously processed.
According to another exemplary aspect of the present invention, each substrate is placed on one of a plurality of first substrate supports when it is placed in the first process chamber, wherein the plurality of substrate supports are operable to vertically translate, thereby vertically translating the substrate placed thereon. For example, the substrate is placed on one of the plurality of supports in a first position when the substrate is placed in the first process chamber, and is subsequently lowered via translating the substrate supports to a second position, wherein contact between the substrate and the first heated plate is established, thereby subjecting the substrate to the first temperature. According to still another exemplary aspect of the invention, the plurality of first supports are operable to rotate about a first axis when in the first position, wherein the first substrate placed on one of the first supports is operable to be rotated to another position associated with the first heated disk. According to yet another exemplary aspect of the invention, the second substrate is consecutively placed on another one of the plurality of first supports prior to the plurality of first supports being lowered to the second position.
Consecutively inserting two or more substrates into the first process chamber significantly limits an amount of time at which the two or more substrates are exposed to the first temperature, thereby advantageously limiting a growth of hillocks in the first layer. According to another exemplary aspect of the invention, the first and second substrates are sequentially processed in the second process chamber, wherein the third predetermined time at which the first and second substrates are subjected to the second temperature is approximately double the first predetermined time at which the first and second substrates are subjected to the first temperature.
According to another exemplary aspect of the present invention, the substrate is subjected to a first temperature in the first process chamber which is lower than the second temperature in the second process chamber. Furthermore, according to still another exemplary aspect of the present invention, deleterious effects associated with transitory RF power of prior art techniques are eliminated by subjecting the substrate a first RF power in the first process chamber and a second RF power in the second process chamber.